The present invention relates to a system for perceptually modeling a video signal which has particular utility in controlling the operation of a variable quantizer for compressing a video-related signal.
Numerous techniques have been proposed for compressing a wide band video signal to enable its transmission through a channel of limited bandwidth, such as a standard 6 MH.sub.z television channel. See, for example, the article by Paul A. Wintz entitled, "Transform Picture Coding" in the Proceedings of the IEEE, Vol. 60, No. 7, pages 809-820, Jul., 1972. Prior art video compression systems typically employ a variable quantizer for effecting bandwidth compression by variably quantizing the transform coefficients of a video-related signal, which signal may represent, for example, the complete video image or just a portion thereof, e.g. a temporally derived difference signal. In any case, compression of the video related signal may be effected by quantizing the transform coefficients using codes of variable bit-length corresponding to different levels of signal resolution. The use of a zero bit-length code may be considered a special case of this type of quantization wherein the corresponding transform coefficients are completely truncated.
Various techniques have been developed for controlling the variable quantization process, i.e. the algorithm employed for determining the bit-length or resolution to be used for representing the various transform coefficients. For example, it is relatively common to quantize the lower order coefficients with more resolution than the higher order coefficients, since low frequency video information is generally considered more important during image reproduction. Such a simplistic approach, however, may or may not provide optimum efficiency in every case. It has been found that quantization efficiency may be improved by controlling coefficient resolution in dependence upon the nature or perceptual characteristics of the video image itself. Due to the complexity of video images or portions of video images, which often comprise combinations of various different perceptual characteristics, accurately modeling or establishing the nature of such images is a particularly difficult task.
It is therefore a basic object of the present invention to provide a novel system for perceptually modeling a video image signal.
It is another object of the invention to provide a system for perceptually modeling a video image signal, which system takes into account the fact that the video image signal may comprise a combination of different perceptual characteristics.
It is a further object of the invention to provide a perceptual modeling system useful for controlling a process in which a video-related signal is variably quantized.